After you refresh your pivot table, the field you placed into the data area disappears, effectively removing the data in your pivot table.
You will run into this behavior when you change the name of the field you placed into the data area. For example, if you created a pivot table and placed a field called Revenue into the data area, your pivot table will show revenue numbers in the data area. If you were to go to your source data and change the Revenue column heading name to "Dollars" and then refresh your pivot table, the numbers in the data area would disappear. This is because when you refreshed your pivot table, it took a new snapshot of your data source and determined that there is no longer a field called "Revenue"and it cannot calculate a field that is not there.
To resolve this issue, open your pivot table field list and simply drag your new field into the data area.